HttpSessionIdResolver supports resolving multiple requested session ids associated with the request - as a consequence, we need to validate the existence of requested session before returning the id. However, if no presented session ids do validate the null is returned, which violates the HttpServletRequest#getRequestedSessionId API.
This commit ensures that if no presented session ids are valid, we respect the HttpServletRequest#getRequestedSessionId API by returning first requested session id.
Resolves: #1229
717e16cb71